Unusual patterns in demand for motherboards lend weight to reports that well-known PC vendors will ship computers with free upgrade coupons for the Windows Vista OS (operating system) in the fourth quarter of this year, analysts say. But the truth remains elusive.

History also supports the claims, since Microsoft and some PC vendors have offered such vouchers in the past ahead of major software or OS upgrades. For example, when Windows XP came out, eMachines offered consumers a coupon for a free upgrade to the OS if they bought a compatible desktop ahead of the launch. That was in 2001.

A few years earlier, Microsoft gave out a 'technological guarantee' coupon for a free upgrade to Office 97 to purchasers of its Office for Windows 95 shipped during Q3 of its fiscal 1997.

Behind the Vista coupon rumours is a fear in the PC industry that users might put off buying a new computer until Vista comes out next year. Ever since Microsoft announced there would be a delay in shipping the OS, the PC industry has sought ideas on how to keep demand for new computers from flagging in the last few months of this year, the important holiday buying season.

Now the rumour mill predicts an October surprise for PC buyers in the form of a free voucher for a Vista upgrade. Unusual motherboard sales patterns support the idea, according to report today by investment bank Goldman Sachs. The company cited a Taiwanese news agency's story on free Vista upgrade coupons as a possible reason that demand for motherboards in the clone market is stronger than demand in the brand-name market. Brand-name PC vendors could be waiting to order more motherboards until later in the year, closer to October, the time when free Vista upgrade coupons might be bundled with new computers, Goldman says.

A few news reports detailing plans for a Vista coupon have also floated across the internet recently. Analysts attending an investor conference at contract notebook PC maker Compal on Wednesday were cited as saying the company's CEO, Ray Chen, revealed plans for a free Vista upgrade coupon to be handed out with PCs sold later this year, most likely in October.

But Compal denied the report.

"Our CEO said our customers, the brand-name computer companies, will offer promotion programs to stimulate market demand. He also said laptops compatible with Vista will be available in October or November, but he did not say anything about a voucher for a Vista upgrade," said Chih-ming Chang, a public relations officer at Compal in Taipei.

Compal is one of the world's largest contract manufacturers of laptop PCs. The company counts Dell and HP among its major customers.